1. Field of the Invention
The present invention relates to a control apparatus for controlling the idling speed of an internal combustion engine provided with a fuel injection device for controlling a flow rate of air flowing through a bypass air passage by which air is supplied into an intake manifold of said internal combustion engine nearby an injection valve.
2. Description of the Prior Art
An internal combustion engine provided with a fuel injection device, specifically an electronically controlled fuel injection device, is provided with a bypass passage which introduces air in an intake passage of said internal combustion engine from upstream side of a throttle valve and discharges a part of said introduced air into the intake passage at downstream side of the throttle valve and remaining part of said introduced air into an intake manifold through an assist air injection port which is provided nearby a fuel injection valve attached to the intake manifold of said internal combustion engine in order to control idling revolution speed of said internal combustion engine. A flow rate control device is connected to this bypass passage to control the flow rate of air to be supplied to said assist air injection port, referring to, for example, temperature of coolant during idling of said internal combustion engine as a parameter, and improve the efficiency of atomization of fuel to be injected from said fuel injection valve, thus ensuring smooth revolution of said internal combustion engine during idling.
Generally speaking, to prevent discharging of unburned evaporative fuel gas from the internal combustion engine, evaporative fuel gas in a fuel tank and blow-by gas in a crank case are supplied to the upstream side of the throttle valve of the intake passage through a charcoal canister and a blow-by reduction device, respectively. Dust particles in suspension in air includes some fine dust which intrudes into the intake passage through an air filter. Therefore, during operation of the internal combustion engine for many hours, said evaporative fuel gas and blow-by gas (hereinafter referred to as "oil mist") and fine dust enter into said bypass passage and may deposit on said assist air injection port to clog the port and thus cause trouble in controlling idling revolution speed of the internal combustion engine.